Interpretive Summary: Gypsy moth (GM) is one of the most serious insect pests of hardwood trees in North America. In recent years, Michigan became the center of a new but rapidly spreading infestation of this pest. In order to bring a new level of noninsecticidal control to GM in Michigan, the introduction of a fungal pathogen that causes significant GM mortality throughout much of range of this insect on the East Coast. Initial surveys of GM populations confirmed the presence of virus carried by all GM populations (but which only periodically causes major mortality); the fungus was not found. During 1991-93, small quantities of the fungus were released into GM populations at 3 sites in Michigan and a monitoring program begun. By the 3rd year of monitoring, the fungus was causing 20-99% mortality at the introduction sites, and had begun to disperse even into the control plots. Egg mass densities were 3-10 times lower in fungus-infested sites than on control plots in 1993. This successful introduction and establishment of the fungus, ENTOMOPHAGA MAIMAIGA, among GM populations in Michigan provides a new tool for management of this pest, and can result in greater overall mortality than that caused by only the virus. The success of this initial study provides an encouraging model for new introductions of the fungus throughout the Michigan range of the pest.

Technical Abstract:
In 1991, late instars of gypsy moth, LYMANTRIA DISPAR (L.), were sampled and diagnosed for infections of the pathogenic fungus ENTOMOPHAGA MAIMAIGA Humber, Shimazu & Soper and for gypsy moth nuclear polyhedrosis virus (NPV) at 50 sit4es in Michigan. Approximately 1500 larvae were collected and reared from these sites, and no infections of E. MAIMAIGA were detected. >From 1991 to 1993, we tested the efficacy of 2 inoculative-release method for E. MAIMAIGA resting spores from Massachusetts to Michigan or by releasing inoculated larvae onto boles of trees. In the 2nd yr after introduction, E. MAIMAIGA became established (9-40% infection) where both inoculation methods were used, and a low level of infection was detected in control plots ().5-2.3%). In the 3rd yr, epizootics of E. MAIMAIGA occurred at all 3 research sites, with the incidence of infection ranging from 20-99%.in both treated and control plots. Infection levels were correlated with precipitation and relative humidity of at least 90% for 2 wk precedin larval sampling. In 1993, egg mass densities at the 3 E. MAIMAIGA study sites averaged 3-10-fold lower than in adjacent oak forest. We found that it is easy to introduce E. MAIMAIGA to new locations even in the midst of an epizootic of gypsy moth NPV and that E. MAIMAIGA reduced gypsy moth populations to levels lower than that caused by NPV alone.